JPS61224536A - Transmission system - Google Patents

Abstract

PURPOSE:To avoid the transmission/reception of a transmission signal from being diabled after application of power and rising of a main controller by applying fault check of all terminal devices and turning on all switches of normal terminal devices at application of power of the main controller. CONSTITUTION:When power is applied to the main controller 1, the main controller 1 initialized each memory and register constituting a transmission control circuit at first under the control of a CPU and closes a relay contact, transmits a realy-on command to a terminal device 3n and detects the short-circuit of a transmission line 2. If short-circuit is detected, it results from the closing of the relay contact 34 of the terminal device 3n receiving the said relay-on command, and since a driver 33 of the terminal device 3n is short-circuited, the address of a faulty terminal device 3n is stored. Similarly, after the detection of relay contact close, short-circuit and storage of terminal number in short- circuit are applied to all terminal devices 3n (n=1-N), the main controller 1 sends the relay-on command to the terminal devices 3, having faulty terminal devices from which short-circuit state is detected.

Description

[Detailed Description of the Invention] [Field of the Invention] The present invention relates to a transmission system in which signals are exchanged between a main control device and a plurality of terminal devices via one transmission line.
In particular, when the power is turned on on the main control unit side or when the system starts up, even if there is an abnormality in any of the terminals that short-circuits the transmission line, all terminals except the abnormal terminal operate normally. Regarding the system.

[Prior Art] As a conventional transmission system, one in which a main control device and each terminal device are multi-drop connected to a transmission line via relay contacts is known (for example, Japanese Patent Laid-Open No. 57-41048,
JP-A-57-188192, etc.). However, these systems have drawbacks such as requiring a separate repeater, being unable to disconnect only a failed terminal, or requiring time to disconnect a failed terminal.

Therefore, the inventors of the present invention first connected a main control device and a plurality of terminal devices to one transmission line in a multi-drop manner, and transmitted signals between the main control device and the terminal devices via this transmission line. In a transmission device for transmitting and receiving data, the transmitting section of the transmitting/receiving circuit connects the main control device and each terminal device to the above transmission line via a switch means, and the receiving section directly connects the above transmission line without going through the switch means. In addition, each of the terminals is provided with means for detecting a short circuit in the transmission line and turning off the switch means, and means for turning on and off the switch means by a control signal from the main control 11 VR device. proposed a transmission system characterized by
-42716).

However, in such a transmission system, if the terminal device is provided with a power source independent of the main control device, the system
l If any of the terminal devices has a short-circuit failure before the power is turned on on the equipment side, the transmission line relays of all the terminal devices that were powered on before the short-circuited terminal device was turned on will turn off the transmission line relays. Therefore, if the main control device side is turned on and the system is started up, there is an inconvenience that the normal transmission signal cannot be received. For example, if the terminal that was last powered on is out of order, all the terminals will be disconnected from the transmission line and the system will not operate at all.

Furthermore, in JP-A No. 59-12657, in each station (8 main controllers or terminals), the output driver of the own station is connected to the transmission line via a relay contact, and the output driver side of the relay contact is connected to the transmission line. By detecting short-circuit abnormalities at A system is disclosed in which the system is turned on.

According to this device, the above-mentioned problem does not occur even when a local power source is provided for each station. but,
This system requires a signal input circuit for detecting the output abnormality, in addition to a signal input circuit for data transmission, for each station, which has the disadvantage of complicating the circuit configuration.

[Object of the invention] The object of the present invention is to solve the problems of the conventional type described above,
In a transmission system where the output end of each terminal is connected to the transmission line via a switch means, and the input end is directly connected, when the main controller is powered on, the main controller sends a switch-on signal to each terminal. If the transmission line is short-circuited due to the switch opening of the terminal device that responded to this signal, the responding terminal device at that time is stored as an abnormal terminal device, and after checking all terminal devices, all switches of the normal terminal device are closed. The idea is to enable normal data transmission to all terminals except for abnormal terminals by turning on the terminal, and to prevent the system from going down when the main controller is powered on or after startup.

[Embodiments of the invention] Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 shows the configuration of a transmission system according to an embodiment of the present invention. In the same figure, 1 is a main control device, a transmission line 2 is connected to this main control device 1, and a terminal device 3 (3+
, 32,...) are connected in a multi-drop manner. Each terminal device 3 also includes a transmission control section 31 that includes a central processing unit (CPU), memory, etc., and performs decoding of transmission signals and detecting short circuits in the transmission line 2, and a transmission control section 31 that is directly connected to the transmission line 2 and connected directly to the transmission line 2.
A receiver 32 relays the transmitted signal etc. to the transmission control unit 31, a driver 32 transmits the transmission signal or reply signal created by the transmission control unit 31 to the transmission line, and an output end of the driver 33 and the transmission line 2. a relay contact 34 inserted in series between the two and controlled on/off by the transmission control unit 31;
It also includes a power cord 35 and the like for supplying power to a power supply section (not shown) provided locally in the terminal.

The transmitting/receiving circuit of the main controller 1 has the same structure as the transmitting/receiving circuit of the terminal device 3, except that a resistor for pulling up the transmission line 2 is added. In the following, main controller 1
Each component of the terminal device 3 shall be represented by a number in the 10s in which the ones digit is the same as that of the common portions of the terminal device 3.

Terminal i! ! To briefly explain the operation of the i3, when the power is turned on, under the control of the transmission control circuit 31, in a terminal device, each memory, register, etc. that constitute the transmission control circuit 31 is initialized, and the relay contact 34 is initialized. After turning on (closed), the next normal operation and transmission line short circuit detection processing are performed.

That is, the transmission control circuit 31 controls each receiver 3
2, the voltage level of the transmission line 2 is monitored. Then, when the voltage on the transmission line 2 becomes L level, the time is counted, and if it is at L level at time t representing the start signal ST, TI<t<T2, normal reception operation is performed. On the other hand, transmission line 2 is connected to II! on T2D between R! When it is at the IL level, it is determined that the transmission line is short-circuited, and each station opens its own relay contact 34.

Next, the terminal device checking operation when the power is turned on in the main controller of the transmission system configured as described above will be explained with reference to the flowchart shown in FIG.

When the power is turned on to the main control device M1, the main control device 1
Under the control of PtJ, first, each memory, register, etc. that constitutes the transmission control circuit 11 is initialized, and the relay contact 14 is initialized.
After turning on, the terminal device check operation, which is a feature of the present invention, starts.

That is, the main control device 1 first transmits a relay-on command to the terminal device 3n, and then detects a short circuit in the transmission line 2. This short circuit in the transmission line 2 may be detected, for example, in the same manner as in the case of the terminal device described above. If a short circuit is detected here, it is due to the relay contact 34 being closed in the terminal device 3n that received this relay-on command, and the driver 33 of the terminal device 3n is short-circuited. The address of the failed terminal device 3n is memorized. In this case, since the short-circuited state of the transmission line continues for a certain period of time or more, the relay contacts 34 of other normal terminals are also disconnected.

On the other hand, if no short circuit is detected at this stage, the main controller 1 increments the terminal device number n and selects the next terminal device 3n.
A relay-on command is sent to terminal 3n+1, and it is determined whether or not terminal 3n+1 is out of order in the same way as was done for terminal 3n described above.

Thereafter, after performing a series of processes such as relay contact opening, short circuit detection, and short circuit terminal number storage for all terminal devices 3n (n=i to N) in the same manner, the main control device 1 detects that the short circuit is detected. A relay-on command is sent to the terminal devices 3 except for the failed terminal device. As a result, the driver 33 of only normal terminal devices is connected to the transmission line 2, and normal data transmission between these terminal devices becomes possible.

[Modifications of Embodiments] The present invention is not limited to the above-described embodiments, and can be implemented with appropriate modifications. For example, in the above-mentioned embodiment, after the abnormality check for all terminals is completed, the relay-on signal is sent again to all terminals except the above terminals. Since the relay contact of the terminal after detecting the abnormal terminal has already been turned on, this relay-on signal may be sent only to the normal terminal before the last abnormal terminal is detected. Furthermore, in this case, if no abnormal terminal is detected, it is not necessary to send out the relay-on signal again.

[Effects of the Invention] As described above, according to the present invention, when the power of the main control device is turned on, all terminals are checked for abnormalities, and all the terminals that are normal are turned on.
It is possible to prevent the worst system failure in which transmission signals cannot be sent or received when the main control device is powered on or after startup.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram of a transmission system according to an embodiment of the present invention, and FIG. 2 is a flowchart for explaining the operation of the system of FIG. DESCRIPTION OF SYMBOLS 1... Main control device, 2... Transmission line, 3... Terminal device, 11, 31... Transmission control unit, 12. 32... Receiver, 13, 33... Driver, 14 .34...
Relay contact, 75, 35...power cord.

Claims (1)

[Claims] 1. A plurality of terminal devices having a switch means for disconnecting the output end of the transmitting section of the device from the transmission line in the event of a short circuit in the transmission line and having a local power source, and a switch-on signal for each terminal device. In a transmission system equipped with a main controller that turns on each switch means by transmitting a After transmitting an on signal to turn on the switch means of the terminal, storing the other terminal when the transmission line is short-circuited as an abnormal terminal, and sending a switch-on signal to all terminals, A transmission system characterized in that a switch-on signal is transmitted to at least a normal terminal device before the detection of the last abnormal terminal device, and all terminal devices other than the terminal device causing the short-circuit abnormality are operated normally.